Modern industrial plant operations generate considerable heatwaste by the rejection of heat from various processes at relatively low temperatures, which low temperatures heretofore have precluded effective recovery of the energy. Typical examples include the warm air discharge from paint curing ovens, heat rejected from condensers of refrigeration units, air exhausted from paint spray booths, or simply ventilating air exhausted to the atmosphere during cold weather conditions.
With the greatly increased cost of energy and its sharply reduced availability, it would of course be highly desirable to recover or utilize energy from every possible source such as the heat normally given off from these sources.
As noted, the chief factor which prevents heat recovery in such situations is the relatively low temperatures of the medium from which the heat must be recovered, such as air exhausted from the paint spray booths. The low temperatures make it difficult to utilize the energy since the necessary temperature differentials for performing useful work in most industrial processes cannot be achieved and also limits the rate of heat transfer from the source at an inadequate rate.
Another major factor is the fact that each of such potential energy sources may yield modest energy levels which may not of itself be sufficient to be directly economically applicable to some other industrial applications.
While it is possible and has heretofore been carried out, the designing of various subsystems which utilized heat energy recovered at one point in the system are not related and, as noted, may in and of themselves be relatively insignificant.
Furthermore, if each energy source were coupled with an energy use process, the necessary balance between the heat energy generated by the energy source and the demand for heat energy required by the application may not be in balance, requiring a supplemental energy source in order to meet the energy demands of the application. This may be occurring at the same time that another heat utilizing subsystem may be in a state of imbalance in which an excess of heat is being recovered over that required by the system in which case the energy must be dissipated and is lost to the overall plant energy equation. In the event a central energy collection and use system is conceived, other difficulties arise.
Firstly, the temperature of the recovery or "collection" heat transfer media from a wide variety of diverse heat energy sources would almost necessarily be at various temperatures in order to achieve maximum energy recovery. The temperature of the respective collection heat transfer media should be preserved to the maximum extent practical during collection and use of the energy. That is, in a central accumulator tank, for example, all of the liquids would be merely collected in a common tank. The higher temperature media would be cooled upon being mixed in the storage tank, compromising the efficiency of heat energy recovery from the relatively higher temperature heat sources.
The second difficulty is in the utilization of the heat energy collected by such a recovery system. Many potential applications for such recovered heat energy may require a heat transfer medium to be within a relatively narrow temperature range and may have varying temperature requirements. Accordingly, any such recovery systems should have a capability for delivering the heat transfer medium through a temperature range such that it may be suited to the particular application.
Yet another difficulty arises from the poor quality of the air in many industrial plants with the air being in a form from which the energy is sought to be reclaimed. Any heat extraction arrangement would of necessity require relatively elaborate filtration prior to circulation through heat exchangers in order to keep maintenance requirements within reason.
However, with the recently imposed, much more stringent air pollution standards, filtration units are often now required in any event such that the heat energy from warmed air within the factory should now allow heat extraction therefrom since such filtration units will provide sufficiently clean air such as to enable use of relatively low cost heat exchanger units.
Accordingly, it is an object of the present invention to provide an energy recovery system for industrial plants or similar applications in which the energy is recovered from a large number of diverse, unrelated secondary heat sources in which the heat energy is recovered from a relatively low temperature media.
It is a further object of the present invention to provide a system for collecting heat energy from such sources and utilizing heat energy with a centralized recovery system, which may also act as a thermal accumulator, smoothing out the heat demands and allowing continuous operation of the related equipment.
It is yet another object of the present invention to provide such centralized heat recovery in which differing temperatures of the collecting heat transfer media are maintained to afford maximum efficiency of the energy recovery process.
It is still another object of the present invention to provide such a centralized energy recovery system in which the heat energy may be delivered to various process applications at controllable temperature levels of the heat transfer media.